So Biden's chance of winning all four of those states, which he did, was 1 in 1075. What an incredibly lucky man! With those odds I hope he bet heavily on himself with his Wilmington bookie.
Apparently this Appendix hasn't been released yet. I'm sure they're polishing the fine details. Lawyer Eugene Volokoh calls it "flim-flammery of the highest order."
This gives a tad more insight, by a anchor on something called Peacock TV, a streaming service of NBCUniversal:
Do you know how big a quadrillion really is? Neither do I. But as Mehdi explains, “one in a quadrillion” is all the math you’re going to need to understand Trump’s chances of being president next term. pic.twitter.com/7Vodiimf4w— The Mehdi Hasan Show (@MehdiHasanShow) December 10, 2020